Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Beyond the read-only/idempotent annotations, the description discloses the important caveat that times are planned timetable times without live delays or cancellations, and that an ambiguous name returns candidates rather than guessing. It does not mention rate limits, auth needs, or result ordering, but the freshness caveat is the key behavioral fact an agent needs.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with the core purpose, then usage, then inputs, then caveats and an example. The input paragraph is dense with useful detail rather than filler, though it is longer than strictly necessary and repeats the 1–40/default range already in the schema.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

An output schema exists, so return format need not be explained. The description covers what the tool does, when to use it versus plan_journey, all input formats, time semantics, and the planned-vs-live data caveat — everything needed to invoke it correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is already 100%, yet the description adds substantial meaning: accepted station formats (name, address, named place, 'geo:lat,lon', find_place place_id), the nearest-stop fallback for addresses/coordinates, and time interpretation rules (ISO 8601, offsets converted, bare '08:00' means today/tomorrow, omit for now). This goes well past the schema's terse field descriptions.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description names a specific verb and resource ('List the next departures from one station or stop') and immediately contrasts itself with the sibling plan_journey. It also defines scope (one station, next departures) which distinguishes it from reachable_area and travel_time_matrix.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

It gives concrete user phrasings ('what leaves from Bern in the next hour', 'when is the next tram from Bellevue'), states an alternative use case for discovering service frequency, and explicitly routes the 'getting somewhere specific' case to plan_journey. When-to-use and when-to-use-something-else are both stated.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.